Spinlyzer used to track a lot of spin players' stats incl. VPIP etc by means of illegal datamining (players were complaining that there was an observer in their every game) until recently when Stars finally found a solution that stopped it from working
So now its data has only historical value and will soon get too old to be relevant.
I haven't bothered to view the data myself, but a Russian €50 Twister (former $60 spin) reg stated a week ago that, according to the 'best hours' feature that was measuring the reg-to-fish ratio (in terms of buy-ins paid) at any given hour of the day, the reg-to-fish ratio at 30s is more than twice bigger (worse) than the one of 15s, at any hour, whereas the difference between 60s-100s (combined) and 30s is 1.3 times.
So the skill leap between 15s and 30s is the biggest.